The large off-the-road pneumatic tires used in heavy construction and earthmoving operations have operating loads and inflation pressures much higher than conventional trucks and lightweight vehicles. Therefore, the radial ply earthmover tires exhibit tremendous load-carrying capacity and need particular reinforcing cords.
JP10131066A discloses a 7×7 cord to meet this load-carrying requirement. JP 2006104636A further discloses a 1×(3+9)+6×(3+9) cord wherein the twisting direction of the strands is the same as the twisting direction of the cord.
Besides, the other concern for the performance of the off-the-road tire is insuring adequate rubber penetration into the cords, which is achieved during the manufacture of the belt layers and in subsequent tire vulcanization. Coupled to this better rubber flow is a desire for higher steel mass and improved wire cut resistance to improve the tires' overall durability. A further requirement for steel cord reinforcing off-road tire is impact resistance capacity, because the surface off the road is not as smooth as the surface of a paved highway. Improved impact resistance capacity not only prolongs the lifetime of the tire but also makes drivers more comfortable when travelling on a bumpy surface.
US2004/0020578A1 discloses a multiple filament diameters in a 7×7 cord design to increase the filament spacings in the cord, which allows better rubber penetration for improved resistance to corrosion as well as superior cut resistance. However, the increased void area in the cord cuts the area of load-bearing steel filaments, which undermines the load-carry capacity of the cord.